Ivan Logashenkofor Mu2e Collaboration

Workshop on e+e- collisions from Phi to Psi, Sep.19-22, 2011Novosibirsk, Russia

Search for cLFVWe had several talks on cLFV already – MEG, COMET, BELLE,…

Why is it interesting?Charged Lepton Flavour Violation in SM is extremely small. Any detectable signal is a sign of New Physics.

Why muons?Copiusly produced

We are trying to measure

Standard Model predicts extremely small value:

( , ) ( , )

( , ) ( , 1)e

A Z e A Z

A Z AR

Z

2* 541

22W,3

3) 10

32Br( k

k ekk

me U

MU

Novosibirsk, 20112 e+e- collisions from Phi to Psi

History of Mu2eThe current best limit was obtained at SINDRUM II experiment (90’s-2000)

Mu2e is the successor of two earlier proposals:

• MELC at Moscow, early 90’s

The main ideas of the experimental design were proposed

• MECO at Brookhaven, early 2000’s

Part of RSVP program, along with KOPIO, search for K->pinunu

At lof of design work and R&D were performed before the program was terminated

Mu2e goal:

137 10e

Au AuR

Au

e

capture

17 (90% c.l.6 10 )e

e

captu

Al AlR

Al re

Novosibirsk, 20113 e+e- collisions from Phi to Psi

Mu2e vs MEG

2( 1)CLFV R L

mL e F

k

2(1 ) L L L L L Le u u d dk

k

“Model-independent” lagrangian:

<< 1magnetic moment

type → e rate ~300X

N → eN rate >> 1

four-fermion interation almost no

contribution to → e

μ → eγ decay and μN → eN conversion are complementary

Mu2e

Mu2e @ProjectX

MEG

SINDRUM IIMEGA

Novosibirsk, 20114 e+e- collisions from Phi to Psi

MEG 2011

Overview of the technique

Stop muons in aluminum

Muons quickly get to 1S orbit

Lifetime of muonic atom is 864 ns

Look for 105 MeV electron

- decay (40%)ee

- capture (60%)XAl

- conversionAl e Al

Hydrogen-like atomBohr radius ≈20 fmNucleus radius ≈4 fm

Most of the background is well below this energy

Use X-rays to monitor number of muons

Novosibirsk, 20115 e+e- collisions from Phi to Psi

Background: Muon decay-in-orbit (DIO)

Free muon In-orbit

Long tail!

For decay-in-orbit , the maximum energy of electron is equal to the energy of conversion electron (≈105 MeV).

The high-energy tail

Need good energy resolution to beat this background!

5

convE E

eeAl Al

Novosibirsk, 20116 e+e- collisions from Phi to Psi

Background: Radiative muon capture (RMC)

This background is mostly low energy, but:

Radiative Muon Capture:• with small BR≈10-5, γ’s from muon captures can have high energy up to

• source of high energy electrons, comparable with DIO at the tail: γ can convert in target to e+e- pair, and electron can get almost all energy

• With good energy resolution and proper choice of target (MZ-1>MZ) this source of background is under control

Al(27,13) Mg(27,12) 1.5 0.1 2n p

Muon capture is the source of many background particles:

2.5 MeV (for Al)N convmm E

Novosibirsk, 20117 e+e- collisions from Phi to Psi

Background: Radiative pion capture (RPC)Muon are produced from pion decays, therefore there are pions in the muon beam.

Radiative Pion Capture:• pions stop at the target and promptly annihilate on the nucleus

• with BR~10-2, γ is produced with energy up to 137 MeV (for Al)

• source of high energy electrons: γ can convert in target to e+e- pair, and electron can enough energy to mimic conversion electron

• This is prompt background, it quickly dies away. Solution: pulsed beam.

(27,13) (27,12)Al Mg

Time distribution of stopped pions in the target

Novosibirsk, 20118 e+e- collisions from Phi to Psi

Overview of the design

Novosibirsk, 20119 e+e- collisions from Phi to Psi

Production Solenoid 4 m longTransport Solenoid 13 m longDetector Solenoid 12 m long

Historical perspective: MELC proposal (1992)

Novosibirsk, 201110 e+e- collisions from Phi to Psi

Production Solenoid

Novosibirsk, 201111 e+e- collisions from Phi to Psi

Extinction

To avoid prompt background, we use pulsed beamThe signal is extremely rare

Need extinction factor 10-10!…and it has to be measured

Use combination of techniques to achieve this factor

Novosibirsk, 201112 e+e- collisions from Phi to Psi

Accelerator

Novosibirsk, 201113 e+e- collisions from Phi to Psi

Mu2e vs NOvA vs g-2

Mu2e can operate concurrently with FNAL neutrino experiments (NOvA)

we use 6 out of 18 Booster batches, which NOvA can’t use during Main Injector cycle

G-2 and Mu2e use the same beam, but in a different mannercannot run concurrently, but there is effort to make it possible to switch between the experiments

Novosibirsk, 201114 e+e- collisions from Phi to Psi

Muon Beam Line

•Negative gradient

magnetic mirrow

no trapped particles

•Uniform field in tracker region

good resolution

•Torroidal field in the transport solenoid

separation/

Novosibirsk, 201115 e+e- collisions from Phi to Psi

Transport Solenoid

Novosibirsk, 201116 e+e- collisions from Phi to Psi

Stopping target

e

17 Al disks, 200 mkm thicknessWhy Aluminum? Perfect for this experiment

•higher Z: larger conversion ratedifferent contributions to the rate

•lower Z: larger lifetimehigher conversion energy

Novosibirsk, 201117 e+e- collisions from Phi to Psi

T-tracker

18 stations x 12 panels x 2x50 straws =21600 straws

5 mm dia. Mylar straws, 15 μm walls, 20 μm Au-plated W wire

200 μm position resolutionNovosibirsk, 201118 e+e- collisions from Phi to Psi

Measuring the momentum

Low energy e- pass undetected

For high energy e- we detect several points on the helix

Novosibirsk, 201119 e+e- collisions from Phi to Psi

CalorimeterLocated downstream of tracker

Main purpose: to provide trigger (1 kHz for E>80 MeV)Provides redundant position, timing and energy data

Possible design:2112 LYSO crystals, 3x3x13 cm3 arranged in 4 vanes. Density 7.3g/cm3, Moliere radius 2.07 cm, Rad. Length 1.14 cm, decay time 40 ns. Light yield relative to NaI 85%.

Two APDs per crystalNovosibirsk, 201120 e+e- collisions from Phi to Psi

Cosmic Ray Shield

Cosmic rays can generate high energy

electrons

Need high suppression factor – a lot of cosmic ray events over 2 year

running period

Combination of passive (magnetized

iron + dirt) and active (scintillation counters) shielding

99.99% coverage Novosibirsk, 201121 e+e- collisions from Phi to Psi

Expected sensitivity

Proton flux 1.8x1013 p/s

Running time 2x107 s

Total protons 3.6x1020 p

Stopped μ per proton 0.0025

μ capture probability 0.61

Time window 0.49

Trigger efficiency 0.80

Selection efficiency 0.19

Sensitivity (90% CL) 6x10-17

Events for Rμe=10-16 4

Estimated background 0.18

Novosibirsk, 201122 e+e- collisions from Phi to Psi

What we expect to see

Novosibirsk, 201123 e+e- collisions from Phi to Psi

Project schedule

e+e- collisions from Phi to Psi Novosibirsk, 201124

July 2005RSVP @BNL cancelled for financial reasons not related to MECO

October 2007

Mu2e LOI submitted to Fermilab

Fall 2008Proposal submitted to Fermilab and receives Stage I approval

November 2009

CD0 status granted

2010-2011 R&D and design, preparation of CDR2012 CD1

~2013 CD2, Start of Solenoid Construction~2018-2020 Start of data taking

Project X

There is proposal to replace FNAL’s Booster with new 8 GeV high-intensity linear accelerator, based on ILC technologies – “Project X”

Project X would feed neutrino and rare decay/high precision experiments

Potential to upgrade Mu2e by factor x100!• set much stronger limits (if there is no signal)

• or use different target materials to study nature of new physics (if there is signal)

Serious upgrade of the detector is required

Novosibirsk, 201125 e+e- collisions from Phi to Psi

ConclusionIn May 2008 P5 (US Particle Physics Project Prioritization Panel) Report stated:

“recommends pursuing the muon-to-electron conversion experiment under all budget scenarios considered by the panel.”

Why?• Mu2e experiment will allow to improve the current limit by 4 orders of magnitude

• if signal is found, it will be an undeniable proof of the New Physics and it will provide data, complementary to LHC

• if no signal is found, it will set constrains much stronger than LHC (up to 1000 TeV mass scale)

• with better muon source and other upgrades, the limits can be improved by another 2 orders of magnitude

Novosibirsk, 201126 e+e- collisions from Phi to Psi